The coating products for walls made up of artificial stones are currently obtained by pouring various very liquid mixtures, usually consisting of inerts (sand), water, cement, additives, colouring, plasticisers, etc., in suitable moulds. The moulds are typically manufactured with polyurethane rubber or with similar materials, as illustrated for example in document WO 2004/062866 A1. The moulds are generally obtained by covering some sample natural stones with the polyurethane rubber, thus obtaining a concave die inside of which the mixture which reproduces the natural stone is poured. With the subsequent hardening of the mixture the finished product is obtained, completely similar to the original stone.
The polyurethane rubber of the moulds, in addition to the fact of perfectly copying the sample to be reproduced, also has the capability of easily detaching from the finished product, obtained from the mixture poured inside of the mould. This is due to the high elastic deformability of the mould, which thus makes it possible to easily free the finished product also in the case of possible undercuts present in the product itself.
The unmoulding is essentially a manual operation and, consequently, it is very expensive. In addition, the capability of easily unmoulding the finished product becomes a negative aspect over time, since the mould loses elasticity and tends to break and/or deform with use, to the point of not being able to be used any longer. Indeed the pieces produced with the broken or deformed mould become incompatible with one another, generating assembly difficulties, since various pieces are no longer capable of coupling with one another in the foreseen manner. The high labour cost for unmoulding and for packing the finished products, to which also the cost of replacing the moulds, which is also high, is added thus leading to a production cost that is substantial for conventional manufacturing plants of artificial stones.
The finished product, generally of the slab-like type, matches the mould both in its lower surface, that is exposed in the coated wall, and its peripheral surface, which has a positive unmoulding surface (see FIGS. 1-3). For such a reason the peripheral or lateral walls A, B, C and D of the product 100, once the latter has been installed, have a peripheral furrow that must be filled with sealing agent and that is clearly visible, with a debatable aesthetic effect. In some cases it is not acceptable for the end buyer, also because it further increases the installation cost.
At the state of the art numerous moulds and relative processes are known for obtaining slab-like products, in particular artificial stones for decorative use, like for example those described in documents WO 2010/069057 A1, EP 2 363 262 A1, WO 99/25933 A1 and US 2008/088063 A1. These documents, however, describe moulds and processes for producing objects that are obtained starting from dry-cast concrete pressed inside metal formworks. On the contrary, the present invention concerns a mould and a plant for the production of stone veneer that is obtained by pouring liquid cement mortar inside the formworks or dies made of polyurethane rubber with high deformability, so as to allow the end product to be subsequently unmoulded.
In the procedures known for obtaining artificial stones starting from liquid mortar or mixtures, the end product is obtained by pouring such liquid mortar or mixtures inside formworks copying the negative of natural stones, made up for example of rocks also with substantial undercuts. At the state of the art the material making up the formwork is flexible and very deformable to such an extent that it is easy to extract the product after it has hardened. This, however, leads to the drawback of wearing and deforming the formwork itself after repeated use. After a certain number of production cycles the formwork becomes useless due to permanent deformation and wearing, which make it necessary for it to be replaced.